1. Field of the Invention
The present invention relates to a direct type of backlight module with a diffuser plate and the manufacturing method thereof, which provides a diffuser plate having a plurality of columnar lenticular lens surfaces for scattering light to provide a uniform and stable panel of a backlight module.
2. Description of the Related Art
A backlight module, is also called a backlight plate, and provides the light for an LCD panel, the emitting light source for which must have the characteristics of high brightness and a long lifespan. The light sources currently used include Cold Cathode Fluorescent Lamp (CCFL), Hot Cathode Fluorescent Lamp, Light Emitting Diode (LED), Electroluminescent panel (EL), of which the CCFL is the most widely used and is of two types, a direct type and a side type.
An LCD has been used in personal information products for close distance use; therefore, requiring a brightness in an approximate range of from 250 to 350 nits. In order to match the requirement for TV long distance viewing, a brightness requirement will be over 500 nits. Because liquid crystals are a self-luminescent material, a light source from a lamp is required. A product under 20″ adopts side light sources, and enhances light uniformity and efficiency by use of a diaphragm of a light guide plate and prism sheet, using 2 to 8 lamp tubes. Because the criteria of brightness and non-visual loss for an LCD TV are higher, a direct type light source becomes the mainstream for large monitor and large TV.
Moreover, the large LCD applications are mainly for notebook PCs and LCD Monitors, that require the characteristics of a backlight module that emphasizes lightweight, thin shape, and small volume. Relatively, while developing a backlight for an LCD TV, the required criteria was developing a brightness of at least over 450 cd/m2, broad viewing angle (current selling products achieving 170 degrees), fresh image contrast (current LCD TV have about 500:1; PDP of about 1000:1), and a suitable lifespan criteria (current product test value is about 60 thousand hours). Based on the above aforementioned criteria, the direct type backlight module has become the technology mainstream for large LCD TV applications. The primary concept of its design is to satisfy the requirement of higher brightness. The illumination module is that of a side light which was used for reducing weight and thickness of the illumination module, where light is scattered uniformly by a direct type light and transformed into a flat light source to enter into the liquid crystal panel. The product structure of a “direct type backlight module” is showing as FIG. 1, which is a structural diagram of a direct type backlight module of the prior art. The direct type backlight module 1′ comprises of a reflector 10′, a plurality of light sources 20′, and a diffuser 30′. Referring to FIG. 1A., which is a diagram illustrating light moving within the prior art diffuser plate, showing that when the light enters into the diffuser plate 30′ and contacts a plurality of light dispersant bodies 32′ within said diffuser plate 30′, the light is subject to non-directional scattering, and is even absorbed by light dispersant bodies 32′.
The characteristics of the technology of the direct type module is as follows:
1. Low Uniformity
The reason is that while using a direct type backlight module is to satisfy the requirement of high brightness, while the size of the module is consideration for relative sacrifice. Therefore, more lamp tubes are used and tend to cause a situation of light and dark stripes, and have a certain influence on uniformity.
2. Thick Module Thickness
Although more lamp tubes increase luminance, the thermal energy resulting from the lamp tubes are relatively high, which can easily cause a change in color under different color temperatures to high sensitivity liquid crystal molecules and color photo resist. Direct type backlight modules usually have a deepened thickness to adjust their depth to match the specification requirements corresponding to the number of lamp tubes and whole luminance.
3. High Light Efficiency
Direct type backlights avoid the side light which causes, in part, light loss and side smear light, and using an aluminum backing plate to reflect stray light to the output windows enhances the whole light energy efficiency.
4. Fewer Assembly Parts Category
It can be observed from FIG. 1 that there is no use of a light guide plate of the side backlight module. Because the function of a light guide plate in the side backlight module is to generate repetitive reflection of a side CCFL light source or LED point light sources by using a dot pattern structure on the light guide plate to derive a uniform light source, direct type light is injected from below, and only requires the diffuser to accomplish uniformity without a light guide plate being included. As for use of a prism sheet part, after increasing the number of lamp tubes and strengthening luminance, removal of the prism sheet can be considered to avoid viewing angle limitations after focusing the light and considering the specification requirements of viewing angle applied to large panels, especially for LCD TVs. On the whole, a direct type backlight module requires less assembly parts than a side type one, but the number of CCFLs is relatively larger.
The direct backlight module is an important device for uniform scattering of light that uses a diffuser plate to replace the light guide plate of a side type light source. The diffuser plate provides light scattering as its primary function, such as in a light box, and light signboard (even a light box used for X-ray examination in a hospital) all use a similar diffuser plate to scatter light uniformly. However, while the diffusion efficiency of early diffuser plates fit the requirement, the light transmission ratio and uniformity is still not enough to use for display applications, having the defect of insufficient brightness. Generally speaking, the transmission rate of the whole light area of these diffuser plates is in a range of from 30% to 50% and that already does not satisfy the requirements, of high brightness for a display. Japanese diffuser plate manufacturers have recently been devoted to solving these defects, by adding different categories of light dispersants and under strict controls of the process, the light transmission efficiency and uniformity have been successfully improved. Although transmission rate has increased in a range from 50% to 70%, the greater transmission rate requirement for LCDs has not satisfied consumers, besides, the cost of light dispersant material still remains high.
Therefore the direct type is the only choice for backlighting of an LCD TV because the characteristics of LCD TV require high uniformity and high efficiency of light diffusion effect to provide stable and uniform light for the liquid crystal panel. The required technology must emphasize high transmission rate and high diffusion of the diffuser plate nowadays.
Therefore, a direct type backlight module with a diffuser plate and its manufacturing method are proposed to solve the defects of low transmission rate and low diffusion caused from too much conventional light dispersant material.